Try using Magical Jelly Bean keyfinder. It should help you find the PC licenses. Here's a bit of information on the app, from the creators website:

The Magical Jelly Bean Keyfinder is a
freeware open source utility that
retrieves your Product Key (cd key)
used to install Windows from your
registry. It allows you to print or
save your keys for safekeeping. It
works on Windows 95, 98, ME, 2000, XP,
Vista, Server 2003, Server 2008,
Office XP, Office 2003, and Office
2007 family of products. It also has a
community-updated configuration file
that retrieves product keys for many
other applications. Another feature is
the ability to retrieve product keys
from unbootable Windows installations.

This is correct and should have been handled as part of 'Due Diligence' when buying out a company and transferring its assets to yourself. During an external audit you will need to provide proof of purchase, certificate of authenticity and a valid code. As we all know, valid codes are 10-a-penny on t'internet, as so do 'they'
–
SzetakSep 18 '09 at 12:50

+1. Product keys are the technical side of license enforcement but they can be worked around and will not convince an organisation like the BSA if they check you out (even WGA/OGA is not enough). Without the legal side of actual inventoried licenses you have no guarantee that the previous company didn't just rip the software off. Best reinstall under your own volume licensing, or else replace with alternatives.
–
bobinceSep 18 '09 at 12:59